Extra-curricular activities quota is an extensive category for students with their exemplary performances and records in various extra curricular activities. Which courses and colleges would be considered under ECA category depends on the particular college only, that means few seats in selected courses are kept for ECA category students.

And sorry but none of the Delhi University college provide admission in B.B.A course through ECA category, only Bachelors in Commerce, Arts and Sciences courses have that facility.
To know about BBA admission in DU, follow this link; DU BBA